Method for producing a contactless chip card

ABSTRACT

A method of producing a contactless chip card ( 10 ) includes first the step of holding a chip ( 14 ), which is provided with terminal pads ( 16   a,    16   b ) on a surface thereof, in a mould defining a chip-card substrate ( 12 ), in such a way that the chip surface provided with the terminal pads is located substantially in the same plane as a chip-card substrate surface defined by the mould. In addition, a chip-card substrate material is introduced into the mould, whereupon a coil structure ( 18 ) is applied by screen-printing a conductive paste onto the chip-card substrate ( 12 ) in such a way that the coil structure ( 18 ) extends up to the terminal pads ( 16   a,    16   b ) on the chip.

FIELD OF THE INVENTION

The present invention refers to a method of producing a contactless chipcard which is supplied with energy and which communicates by means ofelectromagnetic waves.

1. Description of Background Art

Lately, it has become much more common to use contactless chip cardse.g. as car keys or as door keys. Such contactless chip cards permit afast and contact-free opening of doors or also a fast identification ofa specific person.

Contactless chip cards normally comprise on a chip-card substrate amicrochip and an antenna structure. Normally, the chip card is notprovided with an internal power supply so as to prevent the chip cardfrom becoming ineffective when the battery has run down. The chip cardis supplied with electric power in the form of electromagnetic wavesfrom a base station, this being one reason for the fact that inductionantennae or coil antennae are normally used for chip cards. In contrastto dipole antennae, loop antennae permit a more effective coupling in ofelectromagnetic power in the antenna on the chip. This power coupledinto the antenna is rectified for supplying the microchip, which isprovided on the chip card as well, with electric power so that saidmicrochip can transmit a special code e.g. to the door lock of a car orto an identification means so as to accomplish an act coded by saidcode.

The operating principles of coupling electric power into the chip cardand of communication between the microchip and a stationary or mobilestation are known to those skilled in the art and described e.g. in U.S.Pat. No. 5,473,323. This patent describes a method for contactless dataand power transmission between a stationary microstation comprising apair of coils and a means for providing an oscillating clock signal anda mobile microunit comprising one or two coils.

In addition, U.S. Pat. No. 5,449,894 describes a method for operating acontactless chip card which is not provided with a battery and which issupplied with power via a power-transmitting alternating field from awrite/read unit. The bidirectional data transmission is accomplished bymodulation of the power-transmitting alternating field by means of anantenna coil, said power-transmitting field producing a coil current inthe coil and a coil voltage at the coil; an input circuit is coupled toends of the coil for generating a supply voltage from the current in thecoil and a voltage detector is coupled to the ends of the coil fordetecting specific properties of the power-transmitting alternatingfield.

U.S. Pat. No. 5,440,302 describes a device for contactless data andpower transmission, which comprises a stationary part and a mobile part.

2. Description of Prior Art

For producing contactless chip cards, an insulating chip-card substrateis normally used on which a microchip that is capable of carrying outthe desired functions is placed. At a point of the chip-card substratewhich is remote from the microchip or on a separate substrate, thenecessary antenna structures, which are substantially implemented ascoils, are additionally applied e.g. by means of known photolithograhictechniques. For connecting the coil structures to the microchip, bondingwires can be used in the case of known contactless chip cards. Thebonding wires extend from a connection point of a coil to a connectionpoint on the microchip, said bonding wires being produced in the mannerknown by means of a bonding device so as to interconnect the coilstructure and the microchip in an electrically conductive manner.

This method of producing known contactless chip cards is disadvantageousinsofar as expensive bonding devices are required for connecting themicrochip to the antenna structure. In the case of a mass product, and acontactless chip card is such a mass product beyond all doubt, evensmall cost advantages of the product decide whether said product willgain acceptance in comparison with a more expensive competing product.

EP 0756244 A2, which has been published after the priority date of thepresent application, discloses a circuit module and a method ofproducing a circuit module. For embedding an integrated circuit into asupporting substrate, a suitable recess can either be provided or theintegrated circuit can be pressed into the supporting substrate byapplying heat and pressure.

DE 4416697 A1 discloses a data carrier provided with an integratedcircuit. The integrated circuit is connected to at least one coil viacontact elements, said integrated circuit and said contact elementsforming a module and the coil being arranged on a card body. The coil isarranged on an inner layer of the card body, said inner layer being alsoprovided with an opening for receiving the module therein. The module,which comprises at least one integrated circuit with two connections, isintroduced in a previously produced recess of the inner layer.

DE 4431606 A1 discloses a chip-card module for a contactless chip cardand a method of producing the same. A semiconductor chip is arranged ona flexible, non-conductive supporting chip, two ends of anenamelled-wire coil being electrically connected to the semiconductorchip so as to establish a direct connection between said semiconductorchip and the coil ends. The chip is placed on the carrier body and isthen contacted.

DE 44 10 732 A1 discloses both a method of producing a chip card and achip card. The chip card comprises a chip and a coil, said chip and saidcoil being arranged on a common substrate and the coil being formed bylaying a coil wire. The chip is incorporated into the surface of thesubstrate by thermocompression, i.e. by making the surface of thesubstrate soft by means of heat and by pressing the chip into saidsurface, or by “rubbing in” by means of ultrasonic action.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an economy-pricedand reliable method of producing a contactless chip card.

This object is achieved by a method of producing a contactless chipcard, comprising the steps of: holding a chip, which is provided withterminal pads on a surface thereof, in a mould defining a chip-cardsubstrate, in such a way that the chip surface provided with saidterminal pads is located substantially in the same plane as a chip-cardsubstrate surface defined by the mould; introducing a chip-cardsubstrate material into the mould; and applying a coil structure byscreen-printing a conductive paste onto the chip-card substrate in sucha way that the coil structure extends up to the terminal pads on thechip.

The present invention is based on the finding that the connection of thecoil structure to the microchip, which has to be carried out in aseparate step, can be dispensed with, when a coil structure as well as achip are arranged on a common insulating chip-card substrate. Byrealizing the coil structure by the application of a conductive paste,after arranging the chip on the chip-card substrate, in such a way thatthe coil structure extends up to the terminal pads on the chip, it is nolonger necessary to carry out a separate bonding step, since the coilstructure is already connected to the chip.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, a preferred embodiment of the present invention willbe explained in detail making reference to the drawings enclosed, inwhich:

FIG. 1 shows a top view of a contactless chip card which has beenproduced by the method according to the present invention; and

FIG. 2A to 2D show a sequence of steps for producing the contactlesschip card according to FIG. 1.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

FIG. 1 shows a schematic top view of a contactless chip card 10 whichhas been produced by the method according to the present invention. Thecontactless chip card 10 comprises an insulating chip-card substrate 12having arranged therein a chip 14 which is provided with two terminalpads 16 a and 16 b. The terminal pads 16 a and 16 b, respectively, haveconnected thereto the ends of a conductive coil structure 18 havingthree turns in the case of the embodiment shown in FIG. 1. The surfaceof the microchip 14 is normally implemented as an insulating surfacewith the exception of the terminal pads 16 a, 16 b. The conductorsections of the coil structure 18 extending over the chip are thereforeinsulated from said chip.

FIG. 2A to 2D show a cross-sectional view of the contactless chip card10 in a sequence of production steps for said chip card. In a mouldhaving a recess defining the shape of the chip-card substrate, the chip14 is held in the manner known. In the next step, the chip is fixedlyplaced in the chip-card substrate 12 by casting a material suitable forthe chip-card substrate 12 into the substrate mould and by curing saidmaterial. Subsequently, an electrically conductive paste 22 is appliedby means of a mask to the chip-card substrate in which the chip 14 isfixedly accommodated. As can be seen in FIG. 1, the electricallyconductive paste 22 forms, in one operation, the coil structure 18 aswell as the connections 24 to the terminal pads 16 a, 16 b, which haveto be carried out in a separate step in the prior art. The applicationof the electrically conductive paste, which can preferably be anelectrically conductive adhesive, is carried out e.g. by means of theknown screen printing process. The mask defines the coil structure 18 aswell as the two ends of the coil structure which establish theconductive connections 24 with the terminal pads 16 a, 16 b of the chip14. After curing of the conductive paste 22, a cover layer 26 is castanalogously to the chip-card substrate 12, whereupon the chip-cardsubstrate 12 and the cover layer 26 are laminated so as to protect thecontactless chip card against external undesired influences and so as tosecure the coil structure 18 in position.

As can be seen from FIG. 2D, separate fastening of the microchip 14 orof the coil structure 18 is therefore not necessary due to thelamination of the cover layer 26 and of the chip-card substrate 12,since said microchip 14 and said coil structure 18 are fixedly andreliably held at their correct positions relative to one another by theconnections 24 as well as by the cover layer 26.

Due to the fact that the chip 14 is cast into the chip-card substrate12, as can be seen in FIGS. 2A to 2D, it is guaranteed that the chip isarranged essentially without any gap towards the chip-card substrate. Inaddition, this is a simple way of guaranteeing that a main surface ofthe chip, which is provided with the terminal pads, is arranged suchthat the surface thereof is substantially flush with the surface of thechip-card substrate, whereby the screen printing process can be used forapplying the conductive paste so as to produce in one step the coilstructure as well as the connection between said coil structure and thechip in a reliable manner.

If, notwithstanding the above, the main surfaces of the chip 14 and ofthe chip-card substrate 12 are not exactly flush with one another due todeviations caused by the production process, certain tolerances exist inthis respect, since the height of the conductive paste 22 can compensateerrors of alignment within certain limits for reliably establishing theconnections 24 with the terminal pads 16 a, 16 b of the chip 14.

Although the drawings of FIGS. 1 and 2A to 2D do not show any gapbetween the chip 14 and the chip-card substrate 12, this exactproduction precision for casting the chip-card substrate material is notabsolutely necessary either, since with regard to the function of thecontactless chip card it is of no importance when a small amount of theconductive paste 22 penetrates into an existing gap as long as theindividual turns of the coil structure 18 are not short-circuited and aslong as possible high-frequency effects caused by parasitic straycapacitances of the coil structure do not make the coil antennaineffective.

What is claimed is:
 1. A method of producing a contactless chip card(10), comprising the following steps: holding a chip (14), which isprovided with terminal pads (16 a, 16 b) on a surface thereof, in amould defining a chip-card substrate (12), in such a way that the chipsurface provided with said terminal pads is located substantially in thesame plane as a chip-card substrate surface defined by the mould;introducing a chip-card substrate material into the mould; and applyinga coil structure (18) by screen-printing a conductive paste onto thechip-card substrate (12) in such a way that the coil structure (18)extends up to the terminal pads (16 a, 16 b) on the chip.
 2. A methodaccording to claim 1, wherein, after the application of the coilstructure on the chip-card substrate (12), an insulating cover layer(26) is applied on top of said chip-card substrate in such a way thatthe coil structure (18) and the chip (14) are arranged between thechip-card substrate (12) and the cover layer (26).